Date: Special Relativity Extra Questions 1/ - A beam of unknown elementary particles travels at a speed of 2.0 x 10 m/s. When the particles are moving at this speed, their average lifetime is found by experimental measurement to be 1.6 x 10 s. 2/ - 3/ - What is their average lifetime when at rest? A distant star has been measured as moving at a speed of 0.80c away from Earth. If a planet of this star sends radio signals to Earth once every second (according to their timescale), how often would we receive them (according to our time scale)? The rest mass of a proton is 1.67 x 10-27 kg. What would we measure as the mass of a proton moving at 0.90c? 4/ - An astronaut who was 20 years old left to explore the galaxy in 1980, on a spaceship with an average speed of 2.5 x 108 m/s. He returns to Earth in 2020. About how old will he appear to be? 5/ - A 3.0 x 105 kg spaceship is launched with an initial velocity equal to the Earth's escape velocity. Calculate the increase in the mass of the spaceship when launched at this speed. 6/ - Tiny subatomic particles called muons are created in collision between cosmic rays and atoms at the upper limit of our atmosphere. At rest, muons have a mean lifetime of only 2.2 x 10 s, before disintegrating into other particles. What is their mean lifetime, if they travel at 0.99c? a) b) c) Not taking relativity into account, what is the average distance you would expect muons to move, at this speed, before disintegrating? What actual distance, on average, do they move before breaking apart 7/ - Scientist Ludwig Von Drake, while in his laboratory, measures the half-life of some radioactive material which is in a bomb, approaching with speed v. Donald Duck, who is riding on the bomb, also measures the half-life. His answer is a factor of two smaller than Ludwig's. What is the value of v, expressed as a fraction of c? (SIN '79) a) 8/ - The nearest star to Earth is Alpha Centauri, a distance of 4.0 light years away. At what constant velocity must a spacecraft travel from Earth if it is to reach the star in 3.0 years, as measured by the travelers on the spacecraft? How long does the trip take according to the Earth observers? b)